This invention relates to a curable resin composition from which a cured resin having resistance to heat, solvent and moisture, adhering property and electrical properties can be prepared.
With the recent advance in electrical and electronics appliances for communication, household and industry, there has been an increasing demand for simplifying methods of mounting such appliances, and accordingly it has been desired to develop electronics materials of light weight and high performance. Various investigations have been undertaken in the field of polymeric materials in order to meet this demand.
In particular, since circuits of higher density have recently been achieved in printed circuit boards, it has been desired to use materials having between heat resistance, dimensional stability or electrical properties. Usually, copper-clad laminated boards based on thermosetting resins such as phenolic resins or epoxy resins are used as the printed circuit boards. The thermosetting resins previously used, however, generally have the defect of poor electrical properties, especially in the high frequency range.
On the other hand, many thermoplastic resins have excellent electrical properties, and attempts have been made to apply heat-resistant thermoplastic resins to electronics instruments and appliances. However, thermoplastic resins are generally inferior to thermosetting resins in heat resistance, solvent resistance, dimensional stability, etc., and their mechanical properties depend largely on temperature. This generally limits the uses of thermoplastic resins.
Polyphenylene ether resins are thermoplastic resins having excellent mechanical and electrical properties, and they exhibit high heat resistance for thermoplastic resins. An attempt was made to produce a copper-clad material having a polyphenylene ether resin as a substrate by utilizing these properties (Japanese patent publication (Kohkoku) No. 25394/1976). When this copper-clad material is exposed to high temperatures, however, the resin is degraded and its impact strength or toughness is reduced rapidly. Moreover, with increasing temperature, its mechanical strength is reduced, and the material undergoes deformation. Furthermore, with increasing temperature, the adhesion strength of the copper foil decreases to cause undesirable phenomena such as swelling or peeling. Because of these defects, copper-clad materials based on polyphenylene ether resins have not yet gained commercial acceptance.
Polyphenylene ether resins are also widely used in fields which involve contact with city, agricultural and industrial waters by utilizing their strong resistance to acids, alkalies or hot water. But they have very poor resistance to aromatic hydrocarbons and halogenated hydrocarbons. Some methods have therefore been proposed to increase resistance to organic solvents. They include, for example, a method comprising curing a polyphenylene ether resin using a metal alcoholate as a catalyst (Japanese patent publication (Kohkoku) No. 29752/1969); a method comprising adding a crosslinking agent to a polyphenylene ether resin to form a three-dimensional network structure (U.S. Pat. No. 3,396,146); and a method comprising mixing a polyphenylene ether resin with a thermosetting resin, and curing the mixture (Japanese patent publication No. 15519/1975). According to these methods, the catalyst, the crosslinking agent or the thermosetting resin is decomposed at high temperatures (required for molding) which are near the melting point of the polyphenylene ether resin. This results in molded articles which are discolored or degenerated or contain foams. Accordingly, these methods have not yet been accepted commercially.
A method for producing a thermoplastic resin plate which comprises utilizing thermoplastic properties of polyphenylene ether resin without incorporating a thermosetting resin into polyphenylene ether resin has been proposed (Japanese patent publication (Kohkai) No. 156076/1979). However, when soldering is carried out on the thermoplastic resin plate at an elevated temperature, the adhesion strength of the copper foil decreases. Furthermore, when the plate is boiled and then is heated, the plate is blistered and deformed, thereby causing undesirable phenomena, such as peeling of the copper foil.